The present invention relates to a level determination system for an optical character reader.
Generally, an optical character reader has a photoelectric converter comprising a photodiode array of the self-scanning type including a number of photodiodes integrated on a single chip. Respective output levels of the photodiodes are unavoidably different from each other, and it is almost impossible to irradiate the whole surface of the card at a uniform intensity. Therefore, the optical character reader is of low reliability when the respective output signals of the photodiodes are directly quantized with reference to a predetermined sliced level to produce signals "1" and "0" which will be applied to a recognition station. Moreover, when video signals from the photodiode array is amplified with the use of an amplifier of high speed operation, DC characteristics, such as drift, of the high speed operation amplifier will be included within the amplified video signals.
Accordingly, an object of the present invention is to provide a novel level determination system useful for an optical character reader.
Another object of the present invention is to provide a novel network for quantizing video signals generated with the use of output signals from a photodiode array in order to provide "1" and "0" signals to be applied to a recognition stage in an optical character reader.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objectives, pursuant to the present invention, a reference level is determined by scanning a reference portion which is preferably provided along one edge of the card. Amplified video signals corresponding to optical information written on the card are quantized to "1" and "0" signals by comparing among three sliced levels which are 0.5, 0.75 and 0.85 times the reference level. The quantized signals are then applied to a recognition station.